5.7 merc quadrajet idle

[lukecono]

Hey guys, I have a Rochester quadrajet on my merc 5.7 and the idle is never the same. I got the boat and the choke was bypassed and is zip tied open. So of course needs some advanced throttle to start. When I come back to neutral it’s sometimes 1100 rpm’s, once it’s warm off plane back to idle it can be 600 and then it stalls when I’m shifting since it’s so low. If I cut it and fire it up warm again it will be no longer 600, but 1000 or higher at the same engine temp. Puzzling that it’s all over the place. It’s not the throttle cable either because I make sure I’m pulled back to idle screw.

Do I go get it rebuilt and a choke put on it? 275 is how much I was told. And that’s for rebuild.

 

[alldodge]

Warm motor up and remove throttle cable and adjust carb idle to spec. Try to push the carb butterfly closed to ensure idle is set correctly.

Adjust throttle cable barrel so cable just slides back on in place. Remove cable again and rotate barrel on cable one more turn out so when cable is reinstalled the cable will be applying pressure holding butterfly closed

 

[lukecono]

Warm motor up and remove throttle cable and adjust carb idle to spec. Try to push the carb butterfly closed to ensure idle is set correctly.

Adjust throttle cable barrel so cable just slides back on in place. Remove cable again and rotate barrel on cable one more turn out so when cable is reinstalled the cable will be applying pressure holding butterfly closed

So you don’t think a rebuild is necessary? And I can continue to operate without a choke? As u saw in images zip tied open

 

[kenny nunez]

You can forget the choke as there is no place for the original choke stove on that Edelbrock manifold. If you are in the south are just use it during the summer. As AD suggested go over the throttle cable attachment.
Quadrajets like around 3 turns from lightly seated on the idle mixture screws. What is the 600 rpm idle vacuum ? Do you know if the original marine camshaft is still in the engine.? Another thing to look at is the centrifugal advance in the distributor. They sometime will stick and will cause a high idle. Remove the distributor cap and try moving the rotor back and forth. I should spring back. It is not hard to remove the breaker plate to service the fly weights. Sometimes one of the return springs may be broken.
Check the distributor before removing the carburetor. If you ever decide to have it rebuilt Do Not swap it for a rebuilt! Have your original carburetor rebuilt.

 

[alldodge]

Not sure if you need a carb rebuild from your symptoms. If things remain as it was after cable adjust then maybe

 

[lukecono]

You can forget the choke as there is no place for the original choke stove on that Edelbrock manifold. If you are in the south are just use it during the summer. As AD suggested go over the throttle cable attachment.
Quadrajets like around 3 turns from lightly seated on the idle mixture screws. What is the 600 rpm idle vacuum ? Do you know if the original marine camshaft is still in the engine.? Another thing to look at is the centrifugal advance in the distributor. They sometime will stick and will cause a high idle. Remove the distributor cap and try moving the rotor back and forth. I should spring back. It is not hard to remove the breaker plate to service the fly weights. Sometimes one of the return springs may be broken.
Check the distributor before removing the carburetor. If you ever decide to have it rebuilt Do Not swap it for a rebuilt! Have your original carburetor rebuilt.

Hey thanks for the reply! The cam is not original. It’s a slightly bigger one nothing crazy. Can barely even hear a loping sound at idle. I will go ahead and check the cable as AD said. I can move the little black peice around back and forth it has about an 1/8th of movement (enough to change the rpm if it’s sticking). With that said I feel there should be some pre loading done. I haven’t ever played with a distributor and taken off the cap to look inside so I don’t know exactly what your referencing. Do u have a picture ?

And thanks I will rebuild my original one if it comes to that!

 

[lukecono]

Warm motor up and remove throttle cable and adjust carb idle to spec. Try to push the carb butterfly closed to ensure idle is set correctly.

Adjust throttle cable barrel so cable just slides back on in place. Remove cable again and rotate barrel on cable one more turn out so when cable is reinstalled the cable will be applying pressure holding butterfly closed

Hey when you say close the butteryfly, you mean the secondaries ? Since my front ones are zip tied open from no choke.

 

[alldodge]

Hey when you say close the butteryfly, you mean the secondaries ? Since my front ones are zip tied open from no choke.

No the primary
Just want you to make sure the carb is fully closed against the idle adjustment screw

 

[kenny nunez]

It appears that your carburetor is good for the time being. Do as AD suggested. If it still does not want to return to idle then try checking the distributor. Take a picture of your distributor so I can tell you how to check it.

 

[lukecono]

It appears that your carburetor is good for the time being. Do as AD suggested. If it still does not want to return to idle then try checking the distributor. Take a picture of your distributor so I can tell you how to check it.

Okay will do , it’s cold day here in Michigan so I’ll at least get it tomorrow

 

[lukecono]

It appears that your carburetor is good for the time being. Do as AD suggested. If it still does not want to return to idle then try checking the distributor. Take a picture of your distributor so I can tell you how to check it.

Okay thanks! Should that little black peice that’s towards the throttle plate move at all? Because I can give it a good back and forth movement by an eighth inch.

 

[lukecono]

Okay thanks! Should that little black peice that’s towards the throttle plate move at all? Because I can give it a good back and forth movement by an eighth inch.

 

[Scott Danforth]

FYI, for about $60 you can buy everything you need to convert to electric choke.

 

[alldodge]

That should have a bit of play

 

[lukecono]

FYI, for about $60 you can buy everything you need to convert to electric choke.

Good to know, any recommendations?

 

[Scott Danforth]

Good to know, any recommendations?

Just google quadrajet electric choke

 

[todhunter]

Hey when you say close the butteryfly, you mean the secondaries ? Since my front ones are zip tied open from no choke.

He is talking about the throttle plate - what you are talking about is the choke and the air doors. The throttle plates (butterflies) are down at the bottom of the carb. You can see the primary throttle plates if you open the choke and look below the venturis. You can see the secondary throttle plates if you open the air doors.

I agree - never get rid of the original Rochester QJ casting - none of the aftermarket ones compare to the quality of an original casting.

I get all my QJ parts from Cliff's High Performance. Cliff carries standard rebuild parts, and I'm fairly sure he can set you up with the correct electric choke to get you back in business. He also wrote a pretty good book on how to care for and rebuild the QJ. There is also a forum on his site where you can ask questions and get good answers. I fought with my QJ for a couple of seasons, but after reading the books, rebuilding the carb, and putting a fuel pressure regulator on my engine, it runs great.